1. Field of the Invention
The invention pertains to a clutch unit for a motor vehicle with a first clutch, by which a crankshaft of an internal combustion engine, which is supported with freedom to rotate around an axis of rotation, can be connected to a flywheel, also supported with freedom to rotate around the axis of rotation, and with a second clutch, by which the flywheel, which is supported with freedom to rotate around the axis of rotation, can be connected to a transmission shaft, also supported with freedom to rotate around the axis of rotation.
2. Description of the Related Art
A clutch unit of the type described above is known from U.S. Pat. No. 4,410,074, in which the two clutches can be engaged and disengaged by a common actuating means.
The object of the invention is create a clutch unit of the type indicated above which makes it possible to reduce the energy consumption of the motor vehicle regardless of the mode in which the vehicle is being operated and which is also compact and light in weight.
According to the invention, the flywheel is provided with at least one permanent magnet and thus forms the rotor of a crankshaft starter-generator, where the pole field or the pole fields of the permanent magnets can be moved passed the stator coil of the stator of the crankshaft starter-generator, this coil being mounted on an stationary component. Each of the first and the second clutches has its own separately operated actuating means and can be engaged and disengaged either independently of each other or in common.
The integration of the crankshaft starter-generator into the clutches requires only a small amount of space, is associated with only a small amount of weight, and makes it possible to achieve optimum energy utilization.
In the situation in which the first clutch is disengaged and the second clutch is engaged, it is possible for the crankshaft starter-generator to act purely as an electric motor to drive the transmission shaft, during which the internal combustion engine can be idle.
In addition, when the driver brakes the vehicle, the crankshaft starter-generator can be used as an electric brake via the transmission shaft and thus feed electrical energy into the vehicle""s electrical system (recuperation).
This engagement situation can also be used to separate the motor from the transmission so that the gears of the transmission can be shifted. The transmission would in this case remain connected to the crankshaft starter-generator, which can actively synchronize the shifting and thus reduce the time required to shift the gears.
When the vehicle is stopped on a hill, the crankshaft starter-generator can generate enough torque to hold vehicle motionless on the hill. Thus a xe2x80x9chill-holderxe2x80x9d function is obtained.
In the engagement situation in which both clutches are engaged, which corresponds to the normal driving mode of the motor vehicle, the internal combustion engine acts by way of the crankshaft and the two clutches not only to drive the transmission shaft but also to operate the crankshaft starter-generator in its generator mode. In addition, the crankshaft starter-generator can be supplied actively with current when it is operating as an electric motor and thus perform an xe2x80x9coverboostxe2x80x9d function to supplement the power of the internal combustion engine.
The transmission can be shifted up or down preferably in the situation in which the first clutch is engaged and the second clutch is disengaged; so that the vehicle can be started off, first and possibly second gear can be also be engaged in this situation. While the internal combustion engine is idle, it can charge the onboard battery of the motor vehicle via the crankshaft starter-generator.
If both clutches are disengaged, the drive train of the motor vehicle is disconnected both in front of and behind the crankshaft starter-generator. In this situation, the crankshaft starter-generator can act as a freely rotating electric motor and be accelerated to a certain speed by electrical energy from the vehicle""s electrical system. This can be done without a great deal of energy, because the crankshaft starter-generator is free-wheeling. If, after this high speed is reached, the first clutch is then engaged, the mass moment of inertia of the flywheel mass of the rotor of the crankshaft starter-generator accelerates the internal combustion engine to ignition or idle speed. Then the starting-off clutch can also be engaged, and the motor vehicle can be driven normally.
This function also makes stop-and-go driving readily possible.
The crankshaft starter-generator does not have to accelerate the internal combustion engine while operating as a motor; it is instead the mass moment of inertia of the starter-generator which is utilized to start the internal combustion engine. The starter-generator therefore does not have to be designed to deliver maximum power when operating as a motor and can thus be designed for optimum efficiency for operation as a generator. This reduces fuel consumption and makes it possible for the crankshaft starter-generator to be built compactly and in a lightweight manner.
It is also possible, however, for the internal combustion engine to be started while the first clutch is engaged and the second is disengaged.
Another way in which the size of the unit and also the space requirement can be reduced is to direct the pole fields of the permanent magnet radially inward and to surround the stator radially by the rotor to form a generator of the external rotor type.
A compact design can also be achieved by providing the first and/or the second clutch with a clutch disk, which is supported with freedom to rotate around the axis of rotation and which can be actuated axially by the friction surface of a pressure plate, also supported with freedom to rotate around the axis of rotation, the disk thus being pushed against the friction surface of the flywheel.
An especially compact and space-saving design is obtained by locating the first and/or the second clutch radially inside the rotor and the stator.
The first clutch can be mounted axially outside the rotor and the stator, and the diameter of its clutch disk can be larger than that of the second clutch.
Because, with respect to the flow of torque, the first clutch is upstream of the flywheel and the second clutch downstream of it, the first clutch will, in order to avoid slipping, be designed to handle the much greater torque required than the second clutch. The second clutch can be designed to handle merely the small amount of torque applied to it and can thus be easily mounted radially inside the rotor and the stator.
The first clutch must be able to transmit not only the average torque without slipping, but also the peak dynamic torques of the internal combustion engine.
If the rotor is supported rotatably on a tubular part of the stationary component, it is possible for these two parts to be coaxial to each other with a high degree of accuracy, which means that the gap between the rotor and the stator can be made very small. This improves the operating properties of the crankshaft starter-generator and makes it possible to reduce its size.
The rotor bearing can be located axially on the side of the first clutch facing the crankshaft or axially on the side of the second clutch facing the transmission and preferably comprises one or more roller bearings, especially ball bearings. To ensure the effective transmission of torque, one or both clutch disks can carry clutch linings, upon which the flywheel friction surfaces and the pressure plate friction surfaces can act.
Because the first clutch serves essentially only to allow the crankshaft starter-generator to accelerate freely up to high speed and to provide the momentum for starting off, it does not have to offer any special smoothness of operation with respect to starting off or accelerating/decelerating. Thus the clutch linings of the first clutch can be sintered linings, preferably unsprung. The sintered linings can be fade-resistant inorganic sintered linings with a fading friction coefficient of approximately 0.4.
The sintered linings can also be metallic, however. Ceramics and fibrous composites can also be used as alternatives to sintered materials.
Because it is especially important for the second clutch to operate smoothly, to engage gently, and to resist grabbing, the clutch linings of the second clutch are preferably sprung organic linings.
If the clutch disk of the first clutch is connected around its circumference in a torsion-proof manner to the crankshaft, the criteria that smoothness of operation be de-emphasized and that high torque be transmitted are fulfilled.
So that the second clutch will engage gently, it is also useful for the clutch disk of the second clutch to have one or more torsional vibration dampers installed radially between the area of the clutch linings and the transmission shaft.
If the clutch disk of the first and/or of the second clutch is installed with flexibility in the axial direction, axial tolerances between the components which rest against each other can be compensated.
For this purpose, the clutch disk of the first and/or of the second clutch can be mounted on the crankshaft and/or on the transmission shaft with freedom to slide in the axial direction.
In a simple design, the crankshaft and/or the transmission shaft has a coaxial splined shaft part, on which the clutch disk of the first and/or of the second clutch is mounted with freedom to slide in the axial direction, so that the tumbling movements of the crankshaft or of the transmission shaft lead to a displacement of the clutch disk and to the lifting-away of the clutch linings from the friction surfaces assigned to them.
If the clutch disk of the first and/or of the second clutch has an area which pretensions the clutch linings into a position which is at an angle to a radial orientation, the clutch linings will be reliably lifted away from the friction surfaces assigned to them when the clutch is disengaged.
The first and/or the second clutch can preferably be actuated by a release device, which can pivot a ring-shaped diaphragm spring acting on the pressure plate of the clutch in question.
A compact design can be obtained by providing the release device of the first clutch with a push-rod or a pull-rod, guided in sliding fashion through the hollow transmission shaft, which rod can exert a pivoting force on the diaphragm spring.
A compact design can also be obtained by providing the release device of the second clutch with an axial bearing, which surrounds the transmission shaft with play and is free to slide in the axial direction, which axial bearing can exert a pivoting force on the diaphragm spring.
It is preferable in this case to provide a release lever or a pressure cylinder concentric to the axial bearing to actuate the axial bearing and thus to slide it in the axial direction.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.